Bi-directional tape drives, both digital and analog, are well known. The state-of-the-art in digital recording is that digital data should be read immediately after being written, in order to insure that the data has been written correctly. For example, a write-head-module is placed in front of a read-head-module, in the direction of tape movement. These two head modules are preferably formed as a single physical unit; thus, the read and write gaps are closely spaced. This arrangement, however, requires two write modules and two read modules for a bi-directional tape drive. One pair of head modules operate on the tape's odd-number tracks, and the other head module pair operate on the even-number tracks during the opposite direction of tape movement.
While a number of prior art arrangements of this type exist, U.S. Pat. No. 3,942,190 is cited as exemplary. In this device, one group of heads is operable during one direction of tape movement, and another group of heads operates during the opposite direction of tape movement. Since only one group of heads operates at a time, a head switching circuit allows a common amplifier to be used by the operative group of heads.
U.S. Pat. No. 3,813,690 provides a somewhat similar teaching.